Over-the-road or off-road vehicles, such as semi-tractor trailers and construction vehicles, are increasingly utilized to satisfy the transportation and construction needs of our economy. These increased needs result in increased utilization of these vehicles to the point where many are operated seven days a week and upwards of eighteen (18) to twenty (20) hours a day with a two person crew or multiple shift operations. This increased utilization is not simply a vehicle statement, but also includes a human factor as these vehicles are operated by at least a driver and often times by a driving team consisting of two individuals who share the duty of operating the vehicle. Since these vehicles are operated so extensively, increased driver and passenger comfort is essential, both in terms of environment temperature and physical space within the vehicle cab. The need for environmental comfort during warm weather is satisfied through the use of an over-the-road or off-road vehicle air conditioning system, while the physical layout has been accommodated through new ergonomic interior designs, including reduced dash size, to maximize the available room within the vehicle cab for passenger occupation.
Typical over-the-road or off-road vehicle air conditioning systems are of the compressor type. These air conditioning systems utilize a compressor, which is driven by a belt coupled to the engine to compress a refrigerant vapor under high pressure which is then circulated through a condenser to remove heat from the compressed high pressure vapor and change it to a liquid state. The liquid refrigerant is then passed through an expansion valve which reduces the pressure on the refrigerant somewhat. This lower pressure refrigerant is then passed through an evaporator, which permits the return of the refrigerant to the vapor state, thereby removing heat from the air blown thereacross by an in-dash fan.
In a modern over-the-road or off-road vehicle, the main components of the refrigeration system, including the compressor and the condenser, are located remotely from the evaporator which is typically installed behind the dashboard air vents to provide cooling of the cabin air as described above, and from the condenser which is typically mounted with the vehicle radiator in the front of the engine compartment. Since the typical compressor vehicle air conditioning system is a closed loop system, the circulating high pressure refrigerant must be passed from the remotely located components within the engine compartment to the vehicle cab-located evaporator and to the forward engine compartment, radiator located condenser via expensive high pressure refrigeration hoses. A typical installation includes the compressor and condenser in the engine compartment of the over-the-road or off-road vehicle, and utilizes multiple high pressure refrigeration lines to couple these components through the firewall and into the cab behind the dash to the location of the evaporator, and to the radiator area of the engine compartment. Each of these high pressure refrigeration lines require high pressure couplings at each connection for the delivery and return of the high pressure refrigerant in the air conditioning system.
As can well be imagined, both from the above-description as well as from personal experiences with vehicular air conditioning systems, this typical installation arrangement for an over-the-road or off-road vehicle air conditioning system is severely prone to leaks of the high pressure refrigerant. These leaks occur at various locations, but are most frequent at the various couplings of the high pressure hose which routes the high pressure refrigerant from the condenser to the interior of the cab, under the dash, and to the location of the evaporator. Another frequent area for leaks occurs at the various couplings of the high pressure hose which routes the high pressure refrigerant from the compressor to the radiator area located condenser. These leaks result in a reduced efficiency of the air conditioning system, expensive recharging of the system with new refrigerant, as well as a hazard to the environment through the escape of the refrigerant. An increased consciousness of the environmental impact that escaped refrigerant has on the planet, as well as increased government regulation regarding the inadvertent release of refrigeration refrigerant, has placed an increased emphasis on overcoming these problems.
In addition to the problem of leaks within the air conditioning system, the use of this type of system requires that expensive high pressure refrigeration lines be utilized within the engine compartment, and between the engine compartment and the interior of the cab. In addition, expensive high pressure couplings must also be utilized in an attempt to reduce the potential for leaks and catastrophic failure of the air conditioning system due to a failed connection of the high pressure refrigeration lines. Also, because the refrigeration system is not closed until assembly of the vehicle takes place within the manufacturing assembly facility, the use of this type of system further burdens the assembly manufacturer by requiring that the initial purging and charging of the refrigeration system take place within the assembly plant of the vehicle itself. As mentioned above, since the use of refrigerant is a highly regulated process, requiring the manufacturing assembler to charge the refrigeration system greatly increases the cost associated with the manufacture of the vehicle.
In an attempt to overcome many of the above-mentioned problems, several manufacturers of over-the-road or off-road vehicle air conditioning systems have designed self-contained systems which include not only the compressor and condenser, but also the evaporator within a close proximity to one another thereby reducing the potential sources of refrigerant leak. However, such systems require a large dedicated block of space be set aside for the refrigeration system within, or within very close proximity to, the cab of the over-the-road or off-road vehicle. One such system is illustrated by U.S. Pat. No. 5,222,372 issued to Derees, et al. on Jun. 29, 1993 for a MODULAR VEHICLE AIR CONDITIONING/HEATER ASSEMBLY. This patent describes the modular air conditioning assembly as being contained in a housing enclosure which is carried by the vehicle in a recess formed by the interior body panel of the vehicle which separates the engine compartment from the passenger compartment, under the dashboard of the vehicle. However, while such a system may be feasible in a passenger vehicle having a large dashboard, such a system is currently not feasible for an over-the-road or off-road vehicle as there is not enough space under the dash for installation of such a large unit.
Other systems, in an attempt to reduce the distance between the main components of the air conditioning system and the evaporator, have gone to a roof mounted design, such as that described in U.S. Pat. No. 4,217,764 issued to Armbruster on Aug. 19, 1980 for a ROOF MOUNTED MOTOR VEHICLE AIR CONDITIONER. However, these roof-mounted systems are typically quite bulky, and require that a hole be cut into the roof of the vehicle to accommodate the cold air vents. As these systems mount on the roof of the vehicle, they also significantly increase the amount of wind drag over the vehicle. In an effort to reduce this drag, a cowling is often included which also increases the cost of the system. Additionally, the air vents which protrude down from the roof of the vehicle significantly impact the ergonomic design of the cab by reducing interior passenger occupation space, as well as increasing the potential of head injury. Additionally, the increased vibration and noise which may result from operating the refrigeration system directly above the head of the driver and occupant of the over-the-road or off-road vehicle further reduces the desirability of this type of system.